Grafting, phase-inversion and cross-linking controlled multi-stage bulk process for making ABS graft copolymers

ABSTRACT

A method is provided for continuous mass polymerization of acrylonitrile-butadiene-styrene type thermoplastics. The method involves charging a liquid feed comprising a vinylidene aromatic monomer, an unsaturated vinyl nitrile monomer and a synthetic butadiene polymer dissolved therein into a grafting reactor to prereact the liquid mass to form grafted rubber continuous phase polymeric product. The product from the grafting reactor is then charged to a phase inversion reactor where free rigid copolymer in monomer is the only continuous phase, and where dispersed particles of grafted rubber with occluded rigid copolymer and monomer are immediately formed from the product of the grafting reactor. The second polymerization product, which is coming out from the phase inversion reactor, is then charged to a finishing reactor wherein the material is further polymerized to form a third polymerization product which then can be devolatilized to provide a final thermoplastic composition. The process of the present invention provides unique capacity and flexibility in controlling and adjusting rubber grafting and rubber particle morphology. Process conditions can be controlled to produce a high gloss or a low gloss resin product.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods for making rubber reinforcedcopolymers, and more particularly relates to methods for making rubbermodified graft copolymers of monovinylidene aromatic monomers andunsaturated nitrile monomers grafted on a rubbery substrate by masspolymerization.

2. Description of the Related Art

Rubber modified graft copolymers of a monovinylidene aromatic such asstyrene and an unsaturated nitrile such as acrylonitrile havingparticulates of rubber, generally an alkadiene rubber, dispersedthroughout a copolymeric matrix (conventionally referred to as ABSresins) are employed in a wide variety of commercial applications suchas packaging, refrigerator linings, automotive parts, furniture,domestic appliances and toys. It is well known that the physicalproperties of an ABS resin such as toughness (i.e., the combination ofelongation and impact strength), at both room and lower temperatures,are affected by the grafted styrene-acrylonitrile copolymers of therubber substrates and by the size, composition and morphology of thedispersed rubber particles and/or the concentration of the rubbersubstrates in the rubber-reinforced copolymers. For example, to achievethe balance of physical properties required in many applications, therubber particles are necessarily dispersed through the copolymer matrixat a relative size of typically 0.5 microns and 5 microns, typicallyyielding a low gloss product as a result of the rubber sizes being atleast 0.4 microns as the average particle size, more typically greaterthan 0.5 microns.

There are two well known manufacturing processes among many differentbulk (mass) ABS processes. The first one is a multi-zone, continuousplug flow process. The second is a bulk/suspension process. Themulti-zone plug flow bulk HIPS/ABS process was described in early U.S.Pat. Nos. 2,646,418; 2,694,692; 2,727,884 and 3,243,481 and in manyother patents that followed, such as U.S. Pat. Nos. 4,874,815;4,785,051; 4,713,420; 4,640,959; 4,612,348; 4,387,179; 4,315,083;4,254,236; 4,417,030; 4,277,574; 4,252,911; 4,239,863; 4,221,883;4,187,260; 3,660,535; 3,243,481--all of which are incorporated herein byreference.

Multizone plug flow bulk processes include a series of polymerizationvessels (or towers), consecutively connected to each other, providingmultiple reaction zones. Butadiene (BD) rubber (stereospecific) isdissolved in styrene (ST) or in styrene/acrylonitrile (ST/AN), and therubber solution is then fed into the reaction system. The polymerizationcan be thermally or chemically initiated, and viscosity of the reactionmixture will gradually increase. During the reaction course, the rubberwill be grafted with ST/AN polymer (grafted SAN) and, in the rubbersolution, bulk SAN (referred to also as free SAN or matrix SAN ornon-grafted SAN) is also being formed. At a point where the free SAN(i.e. non-grafted SAN) can not be "held" in one single, continuous"phase" of rubber solution, it begins to form domains of SAN phase. Thepolymerization mixture now is a two-phase system. As polymerizationproceeds, more and more free SAN is formed, and the rubber phase startsto disperse itself as particles (rubber domains) in the matrix of theever-growing free SAN. Eventually, the free SAN becomes a continuousphase. This is actually a formation of an oil-in-oil emulsion system.Some matrix SAN is occluded inside the rubber particles as well. Thisstage is usually given a name of phase inversion. Pre-phase inversionmeans that the rubber is a continuous phase and that no rubber particlesare formed, and post phase inversion means that substantially all of therubber phase has converted to rubber particles and there is a continuousSAN phase. Following the phase inversion, more matrix SAN (free SAN) isformed and, possibly, the rubber particles gain more grafted SAN. When adesirable monomer conversion level and a matrix SAN of desired molecularweight distribution is obtained, the reaction mixture is "cooked" at ahigher temperature than that of previous polymerization. Finally, bulkABS pellets are obtained from a pelletizer, after devolatilization wherevolatile residuals are removed.

For the mass/suspension process, U.S. Pat. Nos. 3,509,237; 4,141,933;4,212,789; 4,298,716, describe those processes. A monomer solution ofrubber substrate is charged to a reactor, and polymerization is carriedout to reach a given solids level where phase inversion occurs. Afterphase inversion, the polymerization mixture is transferred to a reactorand mixed with water/suspending agent/surface-active agent.Polymerization is then completed in this suspension system.

Furthermore, U.S. Pat. No. 3,511,895 describes a continuous bulk ABSprocess that provides controllable molecular weight distribution andmicrogel particle size using a "three-stage" reactor system, forextrusion grade ABS polymers. In the first reactor, the rubber solutionis charged into the reaction mixture under high agitation to precipitatediscrete rubber particle uniformly throughout the reactor mass beforeappreciable cross-linking can occur. Solids levels of the first, thesecond, and the third reactor are carefully controlled so that molecularweights fall into a desirable range.

Continuous mass polymerization processes employing continuous-stirredtank reactors have been employed in the production of high impactmodified polystyrene wherein for example a process involving threereaction steps wherein the first step is a continuous-stirred tankreactor, the second step is a continuous-stirred tank reactor, and thethird step is a plug-flow reactor.

In such a system, the first continuous-stirred tank reactor would becharged with styrene monomer having polybutadiene polymer dissolvedtherein, wherein the styrene monomer and polybutadiene polymer would bereacted sufficiently until phase inversion, at which point discreteparticles of rubbery phase would separate from a second phase ofpolystyrene and styrene monomer, this phase inverted product would thenbe charged to a second continuous-stirred tank reactor wherein furthermonomer conversion takes place, followed by reaction of product from thesecond continuous-stirred tank reactor in a plug-flow type reactor toobtain final conversion. There is a desire to employ continuous-stirredtank reactors, due to their superior ability to control temperature andheat transfer in the reactor, in the mass polymerization of ABS typegraft copolymers. However, applicant has discovered that using a firststep involving a continuous-stirred tank reactor wherein phase inversionoccurs does not yield uniform grafting of the rubber and results in anundesired precipitation of rubber particles before high levels ofgrafting onto the rubber are achieved. Inadequate grafting leads to poorproduct performance including reduced levels of impact strength.

Furthermore, different processes of ABS manufacturing give differentproperties to the final ABS products. One of these properties is thesurface gloss of the end products, and technology development to produceABS materials that could meet with different gloss requirements is stillan on-going task for the ABS industry.

The gloss of an ABS product is partially the result of moldingconditions under which the product is manufactured. However, for a givenmolding condition, the rubber particle size (diameter) of the ABSmaterial is a major contributing factor to the gloss. In general but notalways, ABS materials from emulsion processes produce rubber particlesof small sizes (from about 0.05 to about 0.3 microns). Therefore, highgloss products are often made from emulsion ABS materials. On the otherhand, ABS materials from mass processes usually form rubber particles oflarge sizes (from about 0.5 to 5 microns). Therefore, low gloss productsare often made using the bulk ABS materials. Although it is possible toproduce small particles using bulk processes, the gloss and impactresistance balance will be difficult to reach.

In order to combine advantages offered by emulsion and bulk ABSmaterials for better gloss and impact balances, these two type of ABSmaterials are blended at different ratios to obtain bimodal particlesize distributions. For example, U.S. Pat. Nos. 3,509,237 and 4,713,420presented technology of this type so that high surface gloss and goodimpact strength were achieved.

Also, ABS materials of bimodal particle size distributions that gavegloss readings from 80 to 99 percent were directly made from a bulkprocess, described in U.S. Pat. No. 4,254,236. To make this type of bulkABS, two feed streams were simultaneously charged to the reactionsystem. One of the feed streams was a mixture containing rubbersubstrate, monomers and a superstrate (matrix polymer) of the monomers.The other was a monomer solution of the rubber substrate. Another U.S.Pat. No. 3,511,895 described a bulk process where rubber particles areformed by dispersing and precipitating polymeric butadiene rubber asdiscrete droplets in the reaction mixture, leading to bulk ABS of highgloss. With such process conditions, the desirable "cell" morphology ofrubber particles could hardly be obtained, resulting in low impactstrength. Another U.S. Pat. No. 4,421,895 described a continuous processfor relatively small sizes (averages were 0.5 to 0.7 microns) of rubberparticles for bulk ABS. However, those average particle sizes are notuncommon for bulk ABS materials and are still not small enough tocontribute to the high gloss performance. However, efforts have beenmade to produce smaller sizes of rubber particles in bulk processesusing a particle disperser after phase inversion, described in EP 0 376232 A2. The average particle sizes were able to be reduced to a volumeaverage diameter of 0.4 microns. But, the respective gloss value was89%, that was only at the high end of the regular bulk ABS"reduced/lower" gloss range.

Overall, current technology described above has not been able toproduce, by a bulk process alone, ABS materials of rubber particles of"cell" morphology with monomodal particle size distributions and withaverage particle sizes less than 0.3 microns of number average diameter,without compromising impact resistance properties.

To synthesize ABS polymers with high performance by bulk processes,three aspects are essential among many others. These three aspects aregrafting of the rubber substrate prior to phase inversion, particleformation during phase inversion, and cross-linking of the rubberparticle at the completion point of the bulk ABS polymerization.However, the above mentioned bulk ABS processes are somehow deficient bydifferent degrees in controlling and in adjusting the grafting, thephase inversion, and the crosslinking. Accordingly, there is a desire toprovide a continuous mass polymerization process which yields thedesired rubber morphology and maximizes grafting thereby allowing aminimization of rubber use for a given level of property performance.Additionally, there is a desire to provide a bulk process capable forproducing ABS resins of low gloss as well as high gloss.

SUMMARY OF THE INVENTION

The present invention provides a multistage bulk process which involvesreacting in a plug flow grafting reactor a liquid feed compositioncomprising vinylidene aromatic monomer, unsaturated nitrile monomer andrubbery synthetic butadiene polymer to a point prior to phase inversion,reacting the first polymerization product therefrom in acontinuous-stirred tank reactor to yield a phase inverted secondpolymerization product which then can be further reacted in a finishingreactor, and then devolatilized to produce the desired final product.The process permits the formation of high gloss bulk products having arubber morphology which is celluar and which permits the combinedproperties of high gloss and high impact strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a process according to the presentinvention including a plug flow grafting reactor, a continuous stirredtank phase inversion reactor, a boiling type plug flow finishing reactorand a devolatilizer.

DETAILED DESCRIPTION OF THE INVENTION

Theoretically, rubber phase inversion starts to occur when the bulkpolymerization solution reaches a point at which the free SAN phasevolume is equal to the grafted rubber phase volume (the equal phasevolume point). At this point, the formation of a continuous free SANphase (or the disappearance of a dispersed free SAN phase) and theformation of a dispersed grafted rubber phase (or the disappearance of acontinuous grafted rubber phase) are at equilibrium. In a practicalterm, however, the driving force to push the equilibrium towards thedirection of inverting the grafted rubber phase into a dispersed phaseis the free SAN polymerization that increases the phase volume of thefree SAN. Almost all current bulk ABS processes would have to undergothis period in order to obtain rubber particles of bulk morphology (cellmorphology), provided that the rubber is sufficiently grafted with theSAN polymer.

To the contrary, the "equilibrium" period for phase inversion is notrequired and will not appear in the process of the present invention.The dissolved rubber is first given adequate time for grafting to reacha practically maximum level in a grafting reactor. Then, the graftedrubber solution is transferred to a polymerization solution where theexisting continuous phase is the monomer solution of free SAN. Undersufficient agitation, rubber particles of "cell" morphology will startto form within the continuous free SAN phase. In other words, thepresent invention develops a new technology to carry out the graftedrubber phase inversion at a point far beyond the equal phase volumepoint. Therefore, rubber particle size distribution can be varied andcontrolled by changing the molecular weights of the grafted SAN in thegrafting reactor and by changing the molecular weights of the free SANin the existing free SAN continuous phase respectively. Therefore, thisinvention provides great flexibility for rubber particle size control toproduce bulk ABS of large particle size distributions for low gloss andbulk ABS of small particle size distributions for high gloss both withgood impact properties. Nevertheless, this type of flexibility canhardly be achieved in the conventional low gloss bulk ABS processeswithout losing impact properties. Thus, the present invention presentsone fundamental difference in terms of rubber particle formation controltechnology compared with the conventional bulk ABS processes.

The present invention involves a continuous mass polymerization process(also referred to as a bulk polymerization process) for making athermoplastic polymer composition comprising a rubber-modified graftcopolymer and a non-grafted rigid polymer (also referred to as a freerigid polymer). The products can have the particle sizes that arecorresponding to a low gloss characteristic or can have small particlesizes that are corresponding to a high gloss characteristic. One of thepreferred products has a number average particle size of less than 0.3microns, a monomodal particle size distribution, and particles of "cell"morphology, and exhibits high gloss, high impact resistance properties.The "cell" morphology may also be described as a rubber membrane networkof spherical surface with the occluded rigid polymer (SAN) filled in theinterior spaces. Furthermore, with the "cell" morphology, the graftedrigid polymer (SAN) is grafted on both sides of the rubber membranes,i.e., exterior or interior of the rubber particle. The process involvesfeeding a liquid feed comprising vinyl aromatic monomer, unsaturatednitrile monomer and a synthetic butadiene polymer dissolved therein to agrafting reactor to produce graft vinyl aromatic-unsaturated nitrilecopolymer grafted on to diene polymer. The amount of the grafted vinylaromatic-unsaturated nitrile copolymer and average molecular weight canbe adjusted and controlled. Also, non-grafted vinyl aromatic-unsaturatednitrile copolymer with a comparable molecular weight to that of thegrafted vinyl aromatic-unsaturated nitrile copolymer is formed in thegrafting reactor under the same given reaction conditions. The graftingreactor is preferably a plug flow type reactor. Furthermore, thereaction conditions are designed so that phase inversion will not happenat this stage. The grafting reactor produces a first polymerizationproduct which has a level of monomer conversion at this stage which isfrom 5 to 25 percent by weight based on the total weight of monomer inthe feed. The first polymerization product is continuously withdrawnfrom the grafting reactor and is continuously charged to a phaseinversion reactor which is preferably a continuous-stirred tank typereactor wherein phase inversion takes place to yield a phase invertedsecond polymerization product that is produced having a level of monomerconversion of from 10 to 60 percent by weight based on the total weightof monomer in the original liquid feed. The phase inversion starts tooccur when the incoming first polymerization product from the graftingreactor is mixed with the reaction mass in the phase inversion reactor.The second polymerization product is continuously withdrawn from thephase inversion reactor and continuously charged to a finishing reactorwhich is preferably a boiling type plug flow reactor, wherein a thirdpolymerization product is produced having a level of monomer conversionof from 70 to 95 percent by weight based on the total weight of themonomer in the liquid feed. The third polymerization product is thencontinuously withdrawn and continuously charged to a devolatilizer toremove volatile materials and obtain the desired thermoplasticcomposition. The process is able to employ a continuous-stirred tankreactor to control temperature and to control heat transfer during phaseinversion, but is also able to achieve high grafting efficiency by usinga separate reactor prior to phase inversion to achieve high levels ofgrafting.

The present invention provides a mass polymerization process that willallow the expected chemistry to take place at the corresponding stageswith respect to those subjects mentioned above, leading to products ofhigh performance. This invention also provides a flexible productionprocess for different grades of rubber modified graft copolymer. Thematerials produced are generally not transparent in nature, but ratherare generally opaque. However, the opacity of the material is, in mostcases, relatively lower than that of emulsion ABS. The present inventionprovides a novel bulk process technology for ABS materials of low glossand high gloss. One of the preferred products of this process canprovide high gloss and high impact resistance ABS by producing rubberparticles of "cell" morphology with small particle sizes of less than0.3 microns number average diameter and monomodal size distributions.That is, the present invention offers technology to produce rubberparticles with sizes close to those of emulsion particles and withsufficient grafted and occluded vinyl aromatic-unsaturated nitrile (SAN)polymers by a bulk process, leading to high surface gloss and goodimpact resistance for the bulk vinyl aromatic-unsaturatednitrile-alkadiene (ABS) materials.

Generally but importantly, the present invention provides technology ofparticle size control within a broad range, as desired, to produce bulkABS with broad variations in gloss, and with good impact resistancebalance.

The present invention involves a continuous mass polymerization process(as illustrated schematically in FIG. 1) for preparing a thermoplasticpolymer composition comprising a rubber-modified graft copolymer of amonovinylidene aromatic monomer, an unsaturated nitrile monomer and,optionally either with or free of one or more other comonomers, whereina liquid feed composition (12) of a monovinylidene aromatic monomer, anunsaturated nitrile monomer and a rubbery butadiene polymer dissolvedtherein, and optionally a solvent, is charged to a grafting reactor (14)wherein the reactive components of the liquid feed are polymerized toproduce a first polymerization product (16) comprising a graftedbutadiene polymer of vinyl aromatic-unsaturated nitrile grafted ontobutadiene polymer and a non-grafted (free or matrix) vinylaromatic-unsaturated nitrile copolymer. The grafted butadiene polymerand non-grafted polymer are in solution of unreacted monomer (where thegrafted butadiene polymer is the continuous phase), and the level ofmonomer conversion is from 5 to 25 percent by weight based on the totalweight of monomer in the liquid feed composition preferably from 6 to 20percent by weight thereof, and most preferably from 7 to 15 percent byweight thereof. This grafting reactor product (16) (also referred to asthe first polymerization product (16)) is then charged to a phaseinversion reactor (18), which is preferably a continuous-stirred tankreactor (18), containing a reaction mass (20) which has undergone phaseinversion and which contains a first continuous phase of monovinylidenearomatic monomer, unsaturated nitrile monomer and non-grafted copolymersthereof, and a second dispersed phase comprising discrete particles ofgraft copolymer having monovinylidene aromatic-unsaturated nitrilecopolymer grafted onto butadiene polymer. The product from this phaseinversion reactor (18) is the second polymerization product (22) and ithas undergone phase inversion and has a monomer conversion level of from10 to 60 percent by weight based on the total weight of monomer in theliquid feed composition, preferably from 20 to 55 percent by weightthereof, and most preferably from 30 to 45 percent by weight thereof.This second polymerization product (22) from the phase inversion reactor(18) is then charged to a finishing reactor (24), which is preferably aboiling type plug flow reactor (24), wherein polymerization is continueduntil the product (26) from the finishing reactor (24) has a monomerconversion level of between 70 and 95 percent by weight based on thetotal monomer in the liquid feed, preferably a conversion level of from80 to 95 percent by weight thereof and most preferably between 85 and 90percent by weight thereof. The product (26) from the finishing reactor(24), referred to as the third polymerization product (26), can then becharged to a devolatilizer (28) wherein residual monomer (30) andresidual solvents (30) can be removed therefrom to produce a finalnonvolatile thermoplastic polymer composition (32). Monomer conversionis defined as weight percent of monomers converted to solids based onthe total weight of monomers in the liquid feed composition, and isdetermined by quantitative vaporization of unreacted monomers, and maybe calculated as (weight of total solids minus weight of initial rubber)divided by initial weight of monomers in the feed).

In the grafting reactor (14), the butadiene polymer substrates aregrafted not only with desirable amounts of monovinylaromatic-unsaturatednitrile copolymer graft portion but also with desirable molecularweights thereof. By grafting to a point prior to phase inversion in thegrafting reactor (14), which is preferably a plug flow reactor (14), theundesirable precipitation or rubber gel formation of ungrafted andlow-grafted rubber particles is prevented from occurring. Furthermore,the non-grafted monovinylaromatic-unsaturated nitrile copolymer (SAN)formed in the grafting reactor (14) also has "matching" molecularweights with those of the vinyl aromatic-unsaturated nitrile graftportion of the grafted butadiene polymer. The reaction in the graftingreactor (14) is initiator controlled providing preferential monovinylaromatic-unsaturated nitrile copolymer (preferably styrene-acrylonitrilecopolymer) formation rates for the graft portion of the graftedbutadiene polymer compared to the non-grafted monovinyl dienearomatic-unsaturated nitrile (preferably styrene-acrylonitrile)copolymer formation rates. Finally, the overall viscosity of the firstpolymerization product (16) from the grafting reactor (14) is expectedto be as close as possible to the viscosity of the reaction mass (20) inthe phase inversion reactor (18), as evidenced by the molecular weightanalyses of the grafting reactor products and the molecular weightanalyses of the phase inversion reactor products. For making a low glossproduct, the desirable weight average molecular weights of the graftingreactor products are in the range of about 150,000 to 250,000 for bothgrafted and non-grafted vinyl aromatic-unsaturated nitrile copolymer.The desirable weight average molecular weights of the phase inversionreactor products are in the range of about 100,000 to 200,000 for thenon-grafted vinyl aromatic-unsaturated nitrile copolymer. For making ahigh gloss product, the desirable weight average molecular weights ofthe grafting reactor products are in the range of about 200,000 to350,000 for both grafted and non-grafted vinyl aromatic-unsaturatednitrile copolymer. The desirable weight average molecular weights of thephase inversion reactor products are in the range of about 150,000 to200,000 for the non-grafted vinyl aromatic-unsaturated nitrilecopolymer. With the controlled molecular weights as described above,phase inversion of the grafted rubber to form rubber particles ofdesirable sizes occurs rapidly but not immediately or instantaneously inthe phase inversion reactor.

The phase inversion reactor (18), in the form of a continuous stirredtank reactor (18), provides greater uniformity in the reactionconditions under which phase inversion occurs and under which rubberparticles are formed than would be achieved by using a plug-flow reactorduring phase-inversion. Theoretically, the phase inversion reactorprovides an operation condition that causes the incoming grafted rubbercontinuous phase to undergo phase inversion stage where dispersed rubberparticles of "cell" morphology are formed in a continuous non-graftedvinyl aromatic-unsaturated nitrile copolymer phase, which is formed inadvance of the rubber phase inversion. The reaction in the graftingreactor (14) is initiator controlled providing preferential vinylidenearomatic unsaturated nitrile copolymer formation rates for the graftvinylidene aromatic-unsaturated nitrile polymer portion of the graftedbutadiene polymer compared to the non-grafted styrene-acrylonitrilecopolymer formation rates. The reaction mechanism at work in the phaseinversion reactor (18) can be that of thermal or chemical initiationwhich results in the formation of lower molecular weight non-graftedvinyl aromatic-unsaturated nitrile copolymer than was formed in thegrafting reactor (14) thereby assisting in viscosity matching betweenthe first polymerization product (16) of the grafting reactor (14) andthe reaction mass (20) in the phase inversion reactor (18). Preferablythe phase inversion reactor (18) has a polymerization temperaturebetween 120° C. and 150° C. The rubbery synthetic butadiene polymer canbe a butadiene homopolymer or a styrene-butadiene block copolymer. Forthe styrene-butadiene block copolymer, one of the advantages this blockcopolymer may have is that polystyrene blocks could serve as a "storage"mechanism for initiator thereby permitting a greater reaction rate inthe grafting reactor for the grafting of block copolymer than for thebutadiene homopolymers. Furthermore, to produce small sized rubberparticles for high gloss ABS there is an additional important conditionto be acquired in the grafting reactor. That is, a substantially higherweight average molecular weight non-grafted monovinylaromatic-unsaturated nitrile copolymer for the first polymerizationproduct than that for the second polymerization product has to be formedin the grafting reactor, as set out above.

Exemplary of the vinylidene aromatic monomers that can be employed inthe present process are styrene; alpha-alkyl monovinyl monoaromaticcompounds, e.g. alpha-methylstyrene, alpha-ethylstyrene,alpha-methylvinyltoluene, etc.; ring-substituted alkyl styrenes, e.g.vinyl toluene, o-ethylstyrene, p-ethylstyrene, 2,4-dimethylstyrene,etc.; ring-substituted halostyrenes, e.g. o-chlorostyrene,p-chlorostyrene, o-bromostyrene, 2,4-dichlorostyrene, etc.; ring-alkyl,ring-halo-substituted styrenes, e.g. 2-chloro-4-methylstyrene,2,6-dichloro-4-methylstyrene, etc. If so desired, mixtures of suchvinylidene aromatic monomers may be employed.

The vinylidene aromatic monomer is used in combination with at least oneunsaturated nitrile monomer (also referred to as alkenyl nitrilemonomer); e.g., acrylonitrile, methacrylonitrile and ethacrylonitrile.

A liquid feed composition (12) comprising 50 to 90 weight percentmonovinylidene aromatic monomer (which is preferably styrene), 8 to 48weight percent unsaturated nitrile monomer (which is preferablyacrylonitrile) having, 2 to 15% by weight of a butadiene polymerdissolved therein based on the entire weight of the liquid feedcomposition, can be continuously mass polymerized in the present processto produce polyblends of vinylidene aromatic-butadiene-unsaturatednitrile graft copolymers and non-grafted vinyl aromatic-unsaturatednitrile copolymers. Such polyblends can be formed from liquid feedcompositions containing monovinylidene aromatic and unsaturated nitrilemonomers in weight ratios of about 90:10 to 50:50 respectively, andpreferably 80:20 to 70:30 by weight respectively thereof. In addition tothe monomers to be polymerized, the formulation can contain initiatorswhere required and other desirable components such as chain transferagents or molecular weight regulators, stabilizers, etc.

The polymerization may be initiated by thermal monomeric free radicals,however, any free radical generating initiators may be used in thepractice of this invention. Conventional monomer-soluble organicperoxides initiators such as peroxydicarbonates, peroxyesters, diacylperoxides, monoperoxycarbonate, peroxyketals, and dialkyl peroxides orsuch as azo-initiators may be used.

The initiator is generally included within the range of 0.001 to 0.5% byweight and preferably on the order of 0.005 to 0.7% by weight of theliquid feed composition, depending primarily upon the monomer present.

As is well known, it is often desirable to incorporate molecular weightregulators such as alpha-methyl styrene dimer, mercaptans, halides andterpenes in relatively small percentages by weight, on the order of0.001 to 1.0% by weight of the liquid feed composition. From 2 to 20%diluents such as ethylbenzene, toluene, ethylxylene, diethylbenzene orbenzene may be contained in the liquid feed composition to controlviscosities at high conversions and also provide some molecular weightregulation. In addition, it may be desirable to include relatively smallamounts of antioxidants or stabilizers such as the conventionalalkylated phenols. Alternatively, these stabilizers may be added duringor after polymerization. The liquid feed composition may also containother additives such as plasticizers, lubricants, colorants andnon-reactive preformed polymeric materials which are suitable for anddispersible therein.

The preferred synthetic rubbery diene polymers are butadiene polymers(including mixtures of butadiene polymers) which can be dissolved in themonomers of the feed composition, i.e., any rubbery diene polymer (arubbery polymer having a second order transition temperature not higherthan 0° centigrade, preferably not higher than -20° centigrade, asdetermined by ASTM Test D-746-52T) of one or more of the conjugated, 1,3dienes, e.g. butadiene, isoprene, 2-chloro-1,3 butadiene, 1chloro-1,3-butadiene, piperylene, etc. Such diene polymers includecopolymers and block copolymers of conjugated 1,3-dienes with up to anyequal amount by weight of one or more copolymerizable monoethylenicallyunsaturated monomers, such as monovinylidene aromatic monomers (e.g.styrene; an alkylstyrene, such as the o-, m- and p-methyl styrenes,2,4-dimethylstyrene, the ethylstyrene, p-tert-butylstyrene, etc.; analpha-methylstyrene, alpha-ethylstyrene, alpha-methyl-p-methyl styrene,etc.; vinyl naphthalene, etc.); arylhalo monovinylidene aromaticmonomers (e.g. the o-, m- and p-chlorostyrene, 2,4-dibromostyrene,2-methyl-4-chlorostyrene, etc.); acrylonitrile; methacrylonitrile; alkylacrylates (e.g. methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,etc.), the corresponding alkyl methacrylates; acrylamides (e.g.acrylamide, methacrylamide, N-butylacrylamide, etc.); unsaturatedketones (e.g. vinyl methyl ketone, methyl isopropenyl ketone, etc.);alpha-olefins (e.g. ethylene, propylene, etc.); pyridines; vinyl esters(e.g. vinyl acetate, vinyl stearate, etc.); vinyl and vinylidene halides(e.g. the vinyl and vinylidene chlorides and bromides, etc.); and thelike. The diene polymers may also be free of any of the abovecopolymerizable monomers.

Any cross-linking of the diene polymers may present problems indissolving the rubber in the monomers for the graft polymerizationreaction. Therefore, preferably the diene polymers in the feedcomposition are non-crosslinked, linear polymers.

A preferred group of diene polymers are the stereospecific polybutadienepolymers formed by the polymerization of 1,3-butadiene. These rubbershave a cis-isomer content of from 30 to 98% by weight and a trans-isomercontent of from 70 to 2% based on the total weight of the rubber andgenerally contain at least about 85% of polybutadiene formed by 1,4addition with no more than about 15% by 1,2 addition. Mooney viscositiesof the diene polymers (ML-4,212° F.) can range from about 20 to 70 witha second order transition temperature of from about -50° C. to -105° C.as determined by ASTM Test D-746-52T. The most preferred diene polymersare styrene-butadiene block copolymers and butadiene homopolymers.

As used herein the term first stage, second stage, and the third stageof the process corresponds to the grafting reactor (14), the phaseinversion reactor (18), and the finishing reactor (24) respectively.

In more detail, the first stage of the process is the rubber graftingreactor (14), preferably a plug-flow type reactor (14), wherein a liquidfeed composition (12) of butadiene polymer (such as a diblockstyrene/butadiene polymer) solution in vinylidene aromatic monomer andunsaturated nitrile monomer, preferably acrylonitrile and styrenemonomers, and ethyl benzene diluent containing cross-linking inhibitorsand molecular weight regulators (such as alpha-methyl styrene dimer) andinitiators (such as peroxyesters) start the polymerization. The reactioncan also be thermally initiated. Chain transfer agents such asalkyl/aryl thiols may be used. Other non-thiol type of chain transferagents may also be used.

The reaction conditions in the grafting reactor (14) are carefullycontrolled so that diene polymers of the feed composition are givenkinetical preference for graft reaction with the styrene andacrylonitrile monomers to form a styrene-acrylonitrile copolymer graftportion grafted to the diene polymer. At the meantime, the dienepolymers are prevented during the reaction in the grafting reactor (14)as much as possible from cross-linking reactions that form rubber gel orany rubber precipitates. On the other hand, the copolymerization of themonomers (styrene and acrylonitrile) of the liquid feed composition (12)to form non-grafted styrene-acrylonitrile copolymer (also referred asfree SAN) is not kinetically favored under the given reactionconditions. Therefore, a relatively low percent of reacted monomersactually becomes non-grafted SAN polymer. Thus, overall, high graftefficiency and graft yield can be reached by employing a pre-phaseinversion grafting reactor (14), which is preferably a plug flow reactor(14).

At this first stage (14) in the process, the grafted diene polymer isstill dissolved in a continuous liquid phase. The non-grafted vinylaromatic-unsaturated nitrile polymer, however, will appear as smallnon-grafted vinyl aromatic-unsaturated nitrile polymer domains in thediene rubber solution. Phase inversion and rubber particle formation iscontrolled not to occur at this first stage (the grafting reactor). Theliquid feed composition (12) is continuously fed to the grafting reactor(14) (the first stage), while the first polymerization product (16)which is a grafted diene polymer solution is continuously pumped out of(withdrawn from) the grafting reactor (14) to the phase inversionreactor (18) (the second stage of the process). The temperature of thegrafting reactor (14) (the first stage) is preferably from about 80 to120 degree Celsius, and the agitation (by an agitator (34) driven by amotor (36)) is preferably in the range of 30 to 150 rpm. Residence timein the grafting reactor (14) is preferably from 0.5 to 10 hours.

The present invention provides reaction conditions to preferentiallyform grafted vinyl aromatic-unsaturated nitrile (grafted SAN polymerportion of the graft copolymer) much more than the non-grafted vinylaromatic-unsaturated nitrile polymer (non-grafted, SAN polymer) in thegrafting reactor. However, as residence time advances in the graftingreactor, increases in the amount of grafted SAN become less and less,eventually, near zero. On the other hand, the amount of non-grafted SANpolymer in the grafting reactor is ever increasing because of anabundance of vinyl aromatic and unsaturated nitrile monomers. However,the reaction to form non-grafted SAN polymer is controlled as it isunfavorable in the grafting reactor (14). There could be a time point atwhich the total amount of grafted SAN polymer portion equals the totalamount of non-grafted SAN polymer and at which the graft efficiency isexactly 50 weight percent and the respective graft yield at that time isexpected to reach a level of being practically maximum, and as notedabove, increases in the graft yield after that time will be very little.This point is called "cross-point", and the graft efficiency beyond thispoint will no longer increase but decrease, and the graft yield willstay virtually unchanged from this point on.

Therefore, preferably the polymerization conditions to form grafted SANpolymer portion and non-grafted SAN polymer in the grafting reactor (14)are set to operate very close to the "cross-point". Theoretically, thegraft efficiency in this reactor will be close to about 50 weightpercent, and the highest graft yield will be reached. The polymerizationin the grafting reactor (14) is carried out to a total solids level atwhich no phase inversion occurs.

The grafting reactor (14) is preferably a plug-flow type reactor (14),and the size of the reactor is such that it has the residence time ofpreferably between 2 and 3 hours at the desired operating rate. Theplug-flow type grafting reactor (14) is operated liquid full withverticle flow from a feed inlet (38) at the bottom (40) of the reactorto an outlet (42) at the top (44) of the grafting reactor (14). Thereare preferably different temperature control zones in order to controldesired temperature profile throughout the grafting reactor (14). Hotoil is preferred heat transfer medium. Preferably radial agitation isprovided by at a rate of preferably about 60 rotations per minutes butthe agitation rate depends on reactor size.

The liquid feed composition (12) is charged into the bottom (40) of avertical elongated grafting reactor (14) (a plug-flow type reactor (14))which is substantially filled with a liquid mass (46) comprising themonomeric vinylidene aromatic monomer, the ethylenically unsaturatednitrile monomer, the synthetic butadiene polymer, a diluent, and anintermediate grafted polymeric material (grafted butadiene polymer)formed therefrom. The liquid mass (46) becomes more viscous as themonomeric material is progressively polymerized. In other words, asportions of the liquid mass (46) are continuously moved forward in aplug-flow fashion through the elongated grafting reactor (14) and aresubjected to a polymerization temperature and to gentle non-turbulentstirring therein, the liquid mass (46) contains progressively increasingamounts of polymeric solids, and the monomers are progressivelypolymerized therein. The stirring is sufficient to substantiallyovercome the tendency of the liquid mass (46) to channel, but issufficiently non-turbulent so as to minimize back-mixing of the masswithin the grafting reactor (14). The viscous, liquid mass (46) in thegrafting reactor (14) is a continuous rubber solution throughout thegrafting reactor (14) and is not polymerized sufficiently in thegrafting reactor (14) to a level causing phase inversion of the rubbersolution. The first polymerization product (16) from the graftingreactor (14) has a monomer conversion of between 5 and 25 weight percentbased on the total weight of monomer in the liquid feed composition(12), more preferably from 6 to 20 weight percent thereof, and mostpreferably between 7 and 15 weight percent thereof. Preferably thegrafting reactor (14) has a polymerization temperature of less than 120°C., preferably between 90° C. and 110° C.

The first polymerization product (16) is continuously withdrawn from theoutlet of the grafting reactor (14), and is continuously charged to thephase inversion reactor (18), which is preferably embodied by a boilingtype continuous-stirred tank reactor (18). The phase inversion reactor(18) of the polymerization process contains a reaction mass (20) whichhas undergone phase inversion thereby forming discrete particles ofgrafted diene copolymer therein. Also, the phase inversion reactor (18)of the polymerization process contains a continuous phase of monomer,non-grafted rigid copolymer, and optionally solvent. The phase inversionreactor (18) heats the reaction mass (20) sufficiently to cause thereaction mass (20) to boil. The vapors released therefrom are condensedat the top (48) of the phase inversion reactor (48) to form a condensatewhich then is reintroduced into the reaction mass (20). The reactionmass is preferably sufficiently agitated by a stirrer (50) which isdriven by motor (52) to cause substantial back-mixing within the phaseinversion reactor, and, more importantly, to assist the formation ofrubber particles with desirable sizes. The monomer polymerization levelwithin the phase inversion reactor (18) is adequately high to causephase inversion therein, and the monomer conversion level of the secondpolymerization product (22) which is preferably withdrawn via an outlet(56) from the bottom (54) of the phase inversion reactor is between 10and 60 percent by weight based on the total weight of the monomer in theliquid feed composition (12).

In more detail, the second polymerization product (22) is continuouslypumped (by pump (58)) from the phase inversion reactor (18) into thefinishing reactor (24), whereby the total solids level of the secondpolymerization product (22) is preferably in a range of from 20 to 55 wt% based on the entire weight of the second polymerization product (22)and the temperature of the reaction mass (20) is preferably between 120to 140 degree Celsius.

The reaction mass (20) in the phase inversion reactor (18) is at ahigher degree of monomer conversion than the grafting reactor (14) sothat monomer depletion from product (16) of the grafting reactor (14)takes place immediately in the phase inversion reactor (18), leading toa decrease of rubber phase volume. Phase inversion of the incomingrubber solution thus starts to occur. Chain transfer agents (andoptionally other additives) (60) can be used in the phase inversionreactor to regulate molecular weight of the non-grafted vinylaromatic-unsaturated nitrile copolymer so that rubber particles ofdesired sizes will be formed. Furthermore, temperature and total solidslevel and shear imparted through agitation may also be adjusted at thisstage. Residence time in the phase inversion reactor (18) is preferablyin the range of about 1 to 10 hours to ensure the completion of phaseinversion. The agitation is preferably about 20 to 200 rpm to providesufficient shear for the grafted diene polymer to disperse.

The viscosity of the reaction mass (20) is relatively constantthroughout the phase inversion reactor so that rubber particles obtainedare expected to have relatively narrow particle size distribution.Furthermore, the grafted SAN gives the rubber particles good stabilityin the reaction mass (20) as well as sufficient occluded SAN polymerwithin the rubber particles. Therefore, the grafting reactor and thephase inversion reactor provide two separate yet consequently dependentsteps where rubber grafts and rubber particle size can be adjusted,changed, and controlled respectively and variably. That is, thecontrollable rubber grafts and the controllable rubber particle sizesare two essential and important features of the present invention. Thelikely narrow particle size distributions are another important resultof the invention.

The second polymerization product (22) is then continuously charged tothe finishing reactor (24) (the third stage of the process) whichcontains a polymeric mass containing grafted copolymer, non-graftedcopolymer and monomer. The polymeric mass (62) of the finishing reactor(24) is preferably boiled under the reaction conditions given for thisprocess, and vapors therefrom are condensed to form condensate which isthen reintroduced into the polymeric mass (62). The polymeric mass (62)in the finishing reactor is sufficiently agitated (by an agitationdevice (64) powered by a motor (66)) preferably with some degree ofback-mixing, and the third polymerization product (26) from thefinishing reactor (24) is withdrawn from the outlet of the reactorthereof. The finishing reactor has a sufficient temperature andresidence time to result in the product obtained therefrom having amonomer conversion of from between 70 and 95 percent by weight based onthe total weight of monomer in the liquid feed composition (12). Thethird stage product (26) (the third polymerization product (26)) iswithdrawn from the finishing reactor (24) and is charged (by a pump(68)) to a devolatilizer (28) wherein the volatiles (30) (mainly,residual monomer and solvent) from the product of the finishing reactorare evaporated therefrom to produce the final thermoplastic polymercomposition (32) of this process.

The finishing reactor (24) provides for completion of non-grafted vinylaromatic-unsaturated nitrile copolymer polymerizations. The butadienepolymer is cross-linked in the finishing reactor to form crosslinkeddiene rubber. The molecular weight of the non-grafted SAN is regulatedto give sufficient high molecular weight for mechanical properties yetreasonable viscosity for material processing. A package of additives forthermal and oxidative stability, weatherability, and viscositymodification may be added to the reaction mixture at this stage or alater stage. Preferably the finishing reactor has a polymerizationtemperature of greater than about 150° C.

The cross-linking of the grafted diene polymer to form cross-linkedrubber is either thermally initiated or chemically initiated by peroxyfree radical initiators to give the rubber particles a certain degree offirmness and integrity. It should be pointed out that during thedevolatilization, an additional degree of cross-linking will be acquiredby the rubber particles. Undesirable rubber cross-linking levels couldoccur. Therefore, in the finishing reactor, the level of cross-linkingshould be controlled such that the resulting rubber particles will haveonly an adequate degree of cross-linking and will give some room for theadditional cross-linking in the devolatilization stage. In any case,over cross-linking of the rubber particles will bring detrimentaleffects to bulk ABS products. Higher temperatures (about 150 to 180degree Celsius) in the finishing reactor are applied to reach a totalmonomer conversion level of about 70 to 95 wt % preferably 80 to 95weight percent based on the entire weight of the liquid feedcomposition. Preferably residence time in the finishing reactor is about2 to 10 hours, and the agitation preferably is about 5 to 50 rpm.

For practice of the invention, the feed solution is preferably preparedfrom vinyl aromatic monomers, ethylenically unsaturated nitriles,synthetic diene polymer or copolymers such as block copolymers ofconjugated 1,3-dienes, and diluents. To prevent rubber cross-linkingreaction from taking place before phase inversion, rubber crosslinkinginhibitors may also added to the liquid feed composition.

The thermal stability additives which may be used include antioxidantssuch as octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate or2,6-di-t-butyl-4-methylphenol and the like. Flow promoters such as EBSwax (N,N'-ethylene bis(stearamide)) and the like may be present in theliquid feed composition. Diluents such as ethylbenzene may be present inthe liquid feed composition at levels up to 50 percent by weight basedon the total weight of the feed composition, preferably from 5 to 30percent by weight thereof, and more preferably from 15 to 25 percent byweight thereof.

EXAMPLES Example 1

The importance of using a grafting reactor.

This example outlines the importance of using a grafting reactor priorto phase inversion in a CSTR. Experimental work for this process hasbeen performed on a bench-scale (2 lbs/hr throughput) as well as a pilotscale (125 lbs/hr) using a reaction system as described above. Reactionconditions and product mechanical properties are given in the followingtables. Intermediate reactor samples and the finished ABS pellets arecharacterized by different analytical methods, such as opticalmicroscopy, transmission electron microscopy (TEM), phase separation,ozonolysis, molecular weight by GPC (gel permeation chromatography),FT-IR, etc.

The analytical results show that graft yield can be adjusted andcontrolled to achieve high grafting levels in the grafting reactor. Withthe high level of grafting, rubber particle stability is then achievedby forming a phase-inverted mass (which is essentially an oil-in-oilstable emulsion) with particle size being controlled in the phaseinversion reactor. The presence of the grafting reactor leads to goodmechanical (impact) properties of the finished ABS product. Withoutgrafting the rubber mixture before the phase inversion reactor, themechanical properties of the finished ABS are poor.

                  TABLE 1                                                         ______________________________________                                        Feed Compositions                                                             ______________________________________                                        12         pbw SBR rubber                                                     66.0       pbw Styrene                                                        22.0       pbw Acrylonitrile                                                  20         pbw Ethylbenzene (as diluent)                                      ______________________________________                                         pbw: parts by weight                                                     

                  TABLE 2                                                         ______________________________________                                        Reaction Temperatures and Conversion Levels                                   1st Rxr                      3rd Rxr                                          Exit            2nd Rxr               TS                                      Temp °C.                                                                           TS %    Temp °C.                                                                        TS %  Temp °C.                                                                      %                                   ______________________________________                                        With   102.2    15.3    119.4  38.1  164.4  70                                graft-                                                                        ing Rxr                                                                       Without                 122.7  42.5  165    71                                grafting                                                                      Rxr                                                                           ______________________________________                                         TS %: percent total solids by weight                                          Rxr is an abbreviation for reactor                                       

                  TABLE 3                                                         ______________________________________                                        Reactor Grafting and Mechanical Properties of Finished ABS                              Grafting                                                                      Rxr    Melt     Izod    Falling Dart                                          Yield %                                                                              Viscosity                                                                              Impact  Impact                                      ______________________________________                                        With Grafting Rxr                                                                         33%      2038     4.0   29                                        Without Grafting                                                                           0%      2054     1.7    6                                        Rxr                                                                           ______________________________________                                        Graft Yield % is obtained from acetone phase separation analysis.             Graft Yield % means (Weight of grafted SAN)/(Weight of rubber                 modified graft copolymer).                                                    Melt viscosity is measured in accordance with ASTM D3835. It is               reported in poise and is measured at 450° F., 1000/s.                  Izod impact strength, in ft.lbs/in, is measured in accordance with            ASTM D256 method A.                                                           Dart Impact strength, in ft.lbs, is measured in accordance with               ASTM D3039.                                                                   Rxr is an abbreviation for reactor.                                       

Example 2

Example 2 demonstrates the flexibility of the process, e.g. the ease ofpreparing a Bulk ABS with an average particle size of <0.3 microns (highgloss), or a Bulk ABS with low gloss.

It has been shown that gloss in ABS is related to particle size. Glosstends to decrease with increasing particle size. The process asdescribed is flexible enough to produce both high and low gloss productswith the same ABS composition. This is achieved by independentlycontrolling the grafting reactor and phase inversion reactor conditionsin such a way as to adjust the molecular weight of the polymerizing SANcopolymer to different levels at different stages.

The feed formulation for the production of high gloss bulkacrylonitrile-butadiene-styrene graft copolymer was as follows: 12.5 pbw(parts by weight) SBR rubber, 21.9 pbw Acrylonitrile, 65.6 pbw Styrene,20 pbw Ethylbenzene (as a diluent), and 0.02 pbw of a peroxy initiator.

                  TABLE 4                                                         ______________________________________                                        Reaction Conditions for High Gloss Bulk ABS                                           Grafting Reactor                                                                           Phase Inver-                                                                             Finishing                                             Top  Middle  Bottom  sion reactor                                                                           reactor                                 ______________________________________                                        Temp°C.                                                                          109.4  77.2    65    111.8    161.7                                 Agitation, rpm                                                                          60     60      60    30       10                                    Total Solids %                                                                          25                   38                                             ______________________________________                                         The mixture at the outlet of the Grafting reactor represents the reaction     material of which the rubber phase is still the continuous phase and of       which the freeSAN is the dispersed phase. The rubber substrate at this        point has been grafted with SAN, but the phase inversion (to form rubber      particles) does not occur until the mixture is introduced to the phase        inversion reactor.                                                       

                  TABLE 5                                                         ______________________________________                                        Outlet of Grafting Reactor Molecular Weights                                           "High Gloss" ABS                                                                          "Low Gloss" ABS                                          ______________________________________                                        Mw, Graft  306,000       181,000                                              Mw, Rigid  336,000       239,000                                              ______________________________________                                        The molecular weight of the SAN produced in the grafting                      reactor during the production of "low gloss" ABS can be adjusted              by the addition of a suitable chain transfer agent (e.g. alpha-               methylstyrene dimer @ 0.20 pbw based upon the feed                            formulation).                                                                 Because the rubber is a diblock butadiene-styrene copolymer,                  the grafted SAN molecular weight (both number average and                     weight average molecular weight, i.e. Mn, and Mw) are                         averaged down by the styrene block of the rubber, particularly                for the Mn value. However, the free-SAN molecular weights are                 not averaged down and are very close to those of the                          grafted SAN.                                                              

                  TABLE 6                                                         ______________________________________                                        Gloss, Impact, and Rubber Particle Size                                       Data for High Gloss ABS                                                       Gloss*, %                                                                             Impact strength**                                                                          Falling Rubber particle size***,                         60 Degree                                                                             Izod         Dart    Average                                          ______________________________________                                        93.00   4.80         30      0.2338                                           ______________________________________                                        *The specular gloss data were obtained on injection molded                    specimens.                                                                    **The units for Izod impact are ft-lbs/in and for Falling Dart are            ft-lbs                                                                        ***The average rubber particle size was measured directly from a              TEM photomicrograph using a computer program for statistics                   calculations. The rubber particle size (diameter) is presented                as number average (diameter) particle size in micron.                     

We claim:
 1. A bulk resin composition obtained by reacting an organiccontinuous phase comprising vinyl aromatic monomer, unsaturated nitrilemonomer and rubbery diene polymer dissolved in said monomers, said resincomposition comprising a graft copolymer and a rubber free copolymer,said graft copolymer comprising a diene rubber substrate and a vinylaromatic/unsaturated nitrile polymer grafted to said substrate, saidrubber substrate having a number average particle size diameter of notmore than 0.3 microns, said rubber substrate having both interior andexterior surfaces and having a cell morphology defined as a rubbermembrane network of spherical surface with occluded vinylaromatic/unsaturated nitrile copolymer inside the rubber substrate, saidgrafted vinyl aromatic/unsaturated nitrile polymers being grafted onboth the interior and exterior surfaces of the rubber substrate wherebysaid composition has a gloss of greater than 90% at 60 degrees asmeasured by a Gardner Gloss Meter.
 2. The composition of claim 1 whereinsaid composition has a Dynatup energy at maximum load of at least 30foot pounds.
 3. The composition of claim 1 wherein said composition hasa Dynatup total energy of at least 30 foot pounds.
 4. The composition ofclaim 1 wherein said rubber substrate number average particle sizediameter is not more than 0.3 microns.
 5. The composition of claim 1wherein said rubber substrate number average particle size diameter isnot more than 0.25 microns.
 6. The composition of claim 1 wherein saidcomposition combines diene polymer level of from 5 percent by weight to20 percent by weight based on the total weight of the composition. 7.The composition of claim 1 consisting essentially of said graftcopolymer and said rubber free polymer.
 8. The composition of claim 1wherein said vinyl aromatic monomer is styrene, said unsaturated nitrilemonomer is acrylonitrile, and said rubber diene polymer is selected froma group consisting of copolymers and butadiene homopolymers.
 9. Thecomposition of claim 1 wherein said organic phase comprises from 5 to 20weight percent rubbery diene polymer, from 60 to 75 weight percent vinylaromatic monomer, and from 20 to 35 weight percent unsaturated nitrilebased on the combined total weight of said organic phase.